This page is... UNDER CONSTRUCTION
WARNING: I am not an expert on cars, automotive engineering, VW Beetles, beach buggies or anything else discussed in these pages. What I have written is my current understanding of the issues involved in building MY buggy. These opinions are based only on my own research in books and on the web. They, therefore, have no basis in fact, may well be wrong and potentially downright dangerous if taken to be gospel truth. If you intend to use any of this information for any purpose other than pure entertainment, then please get its validity confirmed by someone who knows what they're talking about! You have been warned...
This page contains the following Sections:
A car brake system consists of a brake pedal, master cylinder, rigid and flexible brake lines, front and rear wheel cylinders/calipers, brake shoes/pads and brake drums/disks. When the brake pedal is depressed, the master cylinder pressurises the brake fluid in the entire system to a uniform pressure. This pressure, in turn, applies a force to the wheel cylinders/calipers, which presses the brake shoes/pads against the rotating drums/disks to provide the stopping force. Nice and simple :-)
On a 'normal' road car, with standard wheels and tyres, the front brakes do most of the work, because when the brakes are applied, weight transfers to the front tyres and the rear tyres are unloaded. Since the amount of traction at a wheel is proportional to the load it exerts on the ground the front wheels are far more capable of stopping the car than the rear wheels. Therefore, the braking bias on most road cars assigns about 60% of the braking effort to the front wheels. This is done in two ways; the piston diameter of the front wheel cylinders/calipers is larger than that of the rear cylinders/calipers and the master cylinder, in a dual circuit braking system, acts on the front wheels first and with greater volume than for the rear wheels. In addition to this, the front brakes usually also have a larger brake friction area than the rear wheels to reduce wear, aid cooling and minimise brake fade.
A beach buggy, built for off-road use, is different in several important ways to the above general description of a 'normal' road car; The weight distribution is biased much more to the rear of the car due to the light body and rear mounted engine and gearbox; The rear tyres are much bigger and provide much better grip than the front tyres; The off-road surface provides much less grip than a normal road. With a 'normal' brake set-up, an off-road beach buggy will lock up and slide the front tyres too easily, even on the road, which will result in reduced braking efficiency and loss of steering control. Yikes!
In order to overcome the difficulties of using the 'normal' brake set-up in an off-road beach buggy, it is necessary to change the braking bias so that more of the braking effort is applied to the rear wheels than the front wheels. If this is done, however, additional consideration is needed to improve the performance of the rear brakes, as they weren't designed for this primary braking role. This will involve maximising the size of the brake friction area and the diameter of the brake.
Disk brakes have several advantages over drum brakes; They brake more progressively than drums; They are less prone to brake fade than drums, due to better cooling; They don't trap dirt inside, which minimises brake wear; They dry out much quicker after getting wet, which improves braking performance; They are self adjusting.
Both drum and disk brake set-ups weigh about the same, so there is little advantage either way in terms of unsprung weight.
The disadvantages of disk brakes on an off-road buggy are that they are: Over-kill for the very light weight of the car; Difficult, and therefore expensive, to get with a 5 bolt 205mm pcd pattern, as custom parts must be used because VW never made a 5 bolt front disk brake; More difficult to adjust the front/rear braking bias using stock components; Too biased to the front of the car if used at the front in conjunction with drums at the rear.
Whilst disk brakes have many desirable features for an off-road beach buggy, the low speed, light weight and rear weight bias of a buggy mean that a drum brake set-up will be more than adequate and a lot cheaper than disks.
However, the drum brake backing plates will not fit on the aluminium bearing carriers of the Eagle Performance 3x3 rear trailing arms that I have chosen, as the mounting flange is round, rather than square like the stock VW flange and as it protrudes further than the stock set-up, it interferes with the shape pressed into the brake backing plate.
I will, therefore, use disk brakes all round on my buggy.
Front Disk Brakes.
Rear Disk Brakes.
Brake Pedal Assembly.
Master cylinders.
There are two different types of residual pressure valves which are used in both front and rear disk and drum brake systems as follows:
Note: Residual pressure valves should be fitted as close to the master cylinder as possible.
VW originally fitted 10 psi residual pressure valves to all 3 outlets (2 front and 1 rear) on drum/drum dual circuit master cylinders. When disk/drum master cylinders were introduced, the two front residual pressure valves were replaced with 2 psi units and the single rear 10 psi unit was retained. VW then dispensed with residual pressure valves altogether on later drum/drum master cylinders. The VW residual pressure valves were not integral with the master cylinder but were screw-in units, fitted between the master cylinder outlets and the brake lines.
Click here to see a picture of the stock VW residual pressure valves on a '71/'72 US Super Beetle with drum brakes all round.
Replacement Type 1 dual circuit master cylinders available now do not have any residual pressure valves fitted and the VW type screw-in units don't appear to be available any more.
Luckily, there are several specialist brake component companies that still manufacture 10 and 2 psi residual pressure valves, as pictured above, which fit anywhere in the brake lines.
I will, therefore, fit 10 psi residual pressure valves in both the front and rear brake circuits on my buggy.
There are two different types of proportioning valves which can be used with either disk or drum brakes, both of which are used in the rear brake circuit, as follows:
VW never fitted either type of proportioning valve to the Beetle. However, since I have significantly changed the stock braking bias towards the rear of the car and I don't really know whether the new ratio will be exactly right or not, I will fit an adjustable proportioning valve to the rear brake circuit on my buggy, if necessary, to enable me to compensate for any rear wheel lock-up problems that I might have.
Metering valves (also referred to as 'hold-off' valves) are used in the front (disk) circuit of a disk/drum brake system to prevent the pressure rising in the front disc brake circuit until the pressure at the rear drums has risen sufficiently to overcome the brake shoe return springs. This helps prevent front wheel lock-up by ensuring that the rear brakes are always actuated first.
As I don't intend to use front disk brakes on my buggy, and I've shifted the braking bias to the rear, I don't think I'll suffer from front wheel lock-up and so I shouldn't need one of these valves. However, if I subsequently change the front brakes from drums to disks, it may become necessary to fit one.
Steering brakes, also known as fiddle, cutting, turning or slew brakes are usually hand operated and are used to brake each rear wheel independently. This gives a significantly reduced turning circle, especially off-road, and can also act as a poor man's diff-lock, by braking a spinning rear driving wheel to restore drive to other wheel.
Steering brakes can be either single or dual handle and have vertical or angled (about 45 degrees) handles. Single handle units operate one rear wheel when the lever is pulled and the other rear wheel when the lever is pushed. Dual handle units have a separate lever for each rear wheel, both of which can be either pulled or pushed, depending on which way round it is mounted. Vertical handle units are usually mounted near to the gear lever, whereas units with angled handles are usually mounted between the seats, close to the hand-brake.
Steering brakes are available with either 5/8" cylinders for drum brake systems or 3/4" cylinders for disk brake systems, from companies such as CNC and Jamar.
Typical brake pedal ratios for manual and power assisted foot brakes are 6:1 and 4:1 respectively, whereas steering brakes have a handle ratio of about 12:1, which means that they take relatively little effort to operate.
Steering brakes have a single input from the master cylinder and dual outputs, one to each rear wheel cylinder and are connected up as shown below: (the diagram shows a vertical single handle unit)
If other components are fitted in the rear brake circuit, such as residual pressure or proportioning valves, the steering brake should be fitted down-stream of the other components, so that they are directly connected to the rear wheel cylinders.
Steering brakes have no effect on normal foot brake operation and cannot legally, or practically, be used as a hand brake (aka emergency or parking brake), as they are not independent of the primary brake circuit and lack of any sort of locking mechanism.
Steering brakes can be fitted to road legal vehicles, but must be rendered inoperable on public roads. A common method for doing this is to lock both handles together with a bolt.
Note: Steering brakes cannot be used with a rear axle diff-lock and wouldn't be a good idea with a limited slip differential.
I will, therefore fit a vertical dual handle steering brake close to the gear lever on my buggy.
A hydraulic Park-Lock can be fitted in the rear brake circuit to give far better holding power on steep slopes than the normal Beetle hand brake. This is achieved by maintaining the line pressure in the rear brake circuit to hold the rear brakes on. The Park-Lock is a simple hydraulic valve and no additional electrical or mechanical linkage is required. To actuate the Park-Lock, press and hold the foot brake, push the Park-Lock button down, release the foot brake and it's locked. To release the Park-Lock, press the foot brake again and it opens automatically. The only problem with this type of device seems to be that the pressure required to release the lock must be greater than the pressure when it was locked. So, if the brakes were applied particularly hard when it was locked, then it can be almost impossible to release it, especially if the temperature (and therefore pressure) has risen significantly since it was locked. If this happens, the pressure must be reduced by opening a bleed valve before the lock can be released.
A hydraulic Park-Lock cannot legally be used as a hand brake (aka emergency or parking brake), as it is not independent of the primary brake circuit, although practically it fulfills the same purpose.
Since the Beetle hand brake was pretty good; the buggy is much lighter than a Beetle and I have also upgraded the rear drum brakes to bigger Type 3 units, I don't think I'll need a hydraulic Park-Lock on my buggy.
In a dual circuit braking system, the brake fluid reservoir must be separate (or at lease divided) for each of the circuits, so that a fluid leak in one of the circuits cannot drain the fluid from the reservoir for both circuits.
The SVA test requires that a brake fluid level warning light be fitted to the reservoir so that the driver is alerted to a low brake fluid condition.
The diagram below shows how the components described above will be connected up in my buggy.
